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Terry Coombs[_2_]

"BQ340" wrote in message
...
On 8/5/2013 9:02 PM, wrote:
I was trying to make two rings from copper pipes, 1.625" OD (wall
thickness 0.061") and 2.125" OD (wall thickness 0.035") respectively.
The length of the ring was to be 0.75".

I cut the pipe oversize on my bandsaw. As expected the cut was not
exactly square. I clamped the first ring initially on the inside in my
3-jaw chuck trying to make sure that the sides of the piece were at
right angles to the body of the chuck as determined by a square.

I faced off the first side and deburred it. I reversed the ring and
clamped it the same way with the faced-off part flat against the jaws
base. I faced off the other end to the required dimension. Everything
looked good.

However, when I checked the final product with a square it was obvious
that neither plane of the ring was square to the sides. I did an
additional check with a height gauge with the ring on a flat (well, as
flat as I could get) surface. There was a difference of 0.017" in
height of the ring around the circumference.

I tried a second ring of the same diameter, this time clamping on the
outside. I checked the position with the square in three different
spots. The interesting part was that the fit was square in two of them
but not in the third.

Anyway, the result was almost identical and I got the same result with
the larger ring.

Although the result is adequate for my purposes I would like to know
why I was unable to make the rings properly. Was I not following the
correct procedure? Where in the procedure could the error have
occurred? I have never before had a problem with facing-off being out
of square with the sides.

Thanks.

Michael Koblic,
Campbell River, BC

Copper as you know, is very soft. You can't clamp it very hard before it
distorts & also it will move in the chuck unless you take very light cuts.
You did not say but I assume you deburred it before chucking in the lathe?

Maybe check it with the square after you faced one end but before you
unclamp it to see if it had moved in the chuck during facing?

You would probably need to put it on a mandrel for perfect accuracy.

MikeB

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Email is valid

Yup , mandrel . Bolt in the end with a rubber washer under a regular steel
washer I'd machine the steel with the mandrel , trim the rubber with a
knife/sandpaper . Tighten the bolt , rubber expands and grips the sleeve .
Take light cuts ...
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Snag